Various types of tests related to patient diagnosis and therapy can be performed by analysis of a sample taken from a patient's infections, bodily fluids or abscesses. These assays typically involve automated analyzers onto which vials containing patient samples have been loaded. The analyzer extracts the samples from the vials and combines the samples with various reagents in special reaction cuvettes or tubes. Frequently, the samples are incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination, for example turbidimetric, fluorometric, absorption readings or the like. The measurements allow determination of end-point or rate values from which an amount of analyte may be determined using well-known calibration techniques.
Although various known clinical analyzers for chemical, immunochemical and biological testing of samples are available, analytical clinical technology is challenged by increasing needs for improved levels of analysis. The improvement of analytical sensitivity continues to be a challenge. Furthermore, due to increasing pressures on clinical laboratories to reduce cost-per-reportable result, there continues to be a need for improvements in the overall cost performance of automated clinical analyzers. Often a sample to be analyzed must be split into a number of sample aliquots in order to be processed by several different analytical techniques using different analyzers. Sample analysis continuously needs to be more effective in terms of increasing assay throughput and increasing speed, as well as providing an increased number of advanced analytical options so as to enhance a laboratory's efficiency in evaluating patient samples. In particular, the results of a first battery of assays on a sample often dictate that a second battery of different assays be performed in order to complete or confirm a diagnosis, called reflux or add-on testing. In such an instance, the second battery of assays is often performed with a more sophisticated analytical technique than the first battery so that sample must be shuffled between different analytical laboratories. In addition to increased inefficiency, extra sample handlings increase the possibility of errors.
Automated clinical analyzers are typically controlled by software executed by a computer using software programs written in a machine language like on the Dimension®) clinical chemistry analyzer sold by Dade Behring Inc, of Deerfield, Ill., and widely used by those skilled in the art of computer-based electromechanical control programming. Such a computer executes application software programs for performing assays conducted by the analyzer but it is also required to be programmed to control and track, among other items:    various analytical devices for performing 100+ different assays on different samples like blood, serum, urine and the like;    re-testing and add-on testing of samples when required by prior results;    the patient's identity, the tests to be performed, if a sample aliquot is to be retained within the analyzer;    calibration and quality control procedures;    an incoming and outgoing sample tube transport system;    inventory and accessibility of sample aliquots within an environmental chamber;    washing and cleaning reusable cuvettes;    reagent and assay chemical solution consumption along with time, and date of consumption of all reagents consumed out of each reagent container and assay chemical solutions consumed out of each vial container on a per reagent container, per calibration vial container, per Quality Control container, per assay, and per calibration basis, for specifically defined time periods; and,    scheduling at least 1000 assays per hour.
From the above descriptions of the complex multiple operations conducted within a clinical analyzer, it is apparent that increasing the ability of a single analyzer to perform analytical tests using a relatively large number of different assay formats in a “user-friendly” manner presents much greater challenges than are encountered when an analyzer conducts, for example, only two different assay formats. However, within the clinical diagnostic field there is a continuing need for new and accurate analytical techniques that can be adapted for a wide spectrum of different analytes or be used in specific cases where other methods may not be readily adaptable. Convenient, reliable and non-hazardous means for detecting the presence of low concentrations of materials in liquids is desired. In clinical chemistry these materials may be present in body fluids in concentrations below 10.sup.-12 molar. The difficulty of detecting low concentrations of these materials is enhanced by the relatively small sample sizes that can be utilized. In developing an assay there are many considerations. One consideration is the signal response to changes in the concentration of analyte. A second consideration is the ease with which the protocol for the assay may be carried out. A third consideration is the variation in interference from sample to sample. Ease of preparation and purification of the reagents, availability of equipment, ease of automation and interaction with material of interest are some of the additional considerations in developing a useful assay.
Luminescent compounds, such as fluorescent compounds and chemiluminescent compounds, find wide application in the assay field because of their ability to emit light. For this reason, luminescers have been utilized as labels in assays such as nucleic acid assays and immunoassays. For example, a member of a specific binding pair is conjugated to a luminescer and various protocols are employed. The luminescer conjugate can be partitioned between a solid phase and a liquid phase in relation to the amount of analyte in a sample suspected of containing the analyte. By measuring the luminescence of either of the phases, one can relate the level of luminescence observed to a concentration of the analyte in the sample.
Particles, such as latex beads and liposomes, have also been utilized in assays. For example, in homogeneous assays an enzyme may be entrapped in the aqueous phase of a liposome labeled with an antibody or antigen. The liposomes are caused to release the enzyme in the presence of a sample and complement. Antibody or antigen-labeled liposomes, having water soluble fluorescent or non-fluorescent dyes encapsulated within an aqueous phase vesicle or lipid soluble dyes dissolved in the lipid bilayer of a lipid, have also been utilized to assay for analytes capable of entering into an immunochemical reaction with the surface bound antibody or antigen. Detergents have been used to release the dyes from the aqueous phase of the liposomes. Chemiluminescent labels offer exceptional sensitivity in ligand binding assays, but one or more chemical activation steps are usually needed. Fluorescent labels do not have this deficiency but are less sensitive.
U.S. Pat. Nos. 5,340,716 and 5,709,994 discloses a method for determining an analyte in a highly sensitive assay format known as a Luminescent Oxygen Channeled Immunoassay (LOCI) using a label reagent comprising a first specific binding pair member associated with a particle having a photosensitizer capable upon activation of generating singlet oxygen and a chemiluminescent compound capable of being activated by singlet oxygen such that upon activation of the photosensitizer, singlet oxygen is generated and activates the chemiluminescent compound, wherein the first specific binding pair member is capable of binding to the analyte or to a second specific binding pair member to form a complex related to the presence of the analyte; the photosensitizer is activated and the amount of luminescence generated by the chemiluminescent compound is detected and related to the amount of analyte in the sample.
U.S. Pat. No. 5,807,675 discloses a method for determining an analyte in a less sensitive assay format known as a Fluorescent Oxygen Channeled Immunoassay (FOCI) using a photosensitizer capable in its excited state of generating singlet oxygen, wherein the photosensitizer is associated with a first specific binding pair member in combination with a photoactive indicator precursor capable of forming a photoactive indicator upon reaction with singlet oxygen, wherein the photoactive indicator precursor is associated with a second specific binding pair member. The combination is irradiated with light to excite the photosensitizer, and in a final step, the fluorescence is measured and related to the amount of the analyte in the sample.
Homogeneous immunoassays in which it is unnecessary to separate the bound and unbound label have previously been described for small molecules. These assays include SYVA's FRAT assay, EMIT® assay, enzyme channeling immunoassay, and fluorescence energy transfer immunoassay (FETI); enzyme inhibitor immunoassays (Hoffman LaRoche and Abbott Laboratories): fluorescence polarization immunoassay (Dandlicker), among others. All of these methods have limited sensitivity, and only a few including FETI and enzyme channeling, are suitable for large multiepitopic analytes. Heterogenous immunoassays in which a separation step is required are generally useful for both small and large molecules. Various labels have been used including enzymes (ELISA), fluorescent labels (FIA), radiolabels (RIA), chemiluminescent labels (CLA), etc. Clinical analyzers in which such homogeneous and heterogenous immunoassays are commercially available and these are generally quite complex. See for example, U.S. Pat. Nos. 6,074,615 and 5,717,148 and 5,985,672 and 5,635,364. From a consideration of patents such as these, it becomes obvious that many challenges are created when clinical analyzers having automated immunoassay systems are to be enhanced in capability with the additional automated ability to perform sensitive Luminescent Oxygen Channeled Immunoassays.